Welcome to HVAC-Talk.com, a non-DIY site and the ultimate Source for HVAC Information & Knowledge Sharing for the industry professional! Here you can join over 150,000 HVAC Professionals & enthusiasts from around the world discussing all things related to HVAC/R. You are currently viewing as a NON-REGISTERED guest which gives you limited access to view discussions

To gain full access to our forums you must register; for a free account. As a registered Guest you will be able to:

Participate in over 40 different forums and search/browse from nearly 3 million posts.

So, let me get this straight. I am going to find my supply wet bulb, return wet bulb and my static pressure..(NO!) that will give me the the BTU per pound of dry air. subtract the two, to get the difference. Use the (enthalpy change) difference in equation(total heat removed=CFMx4.5xEnthalpyChange)

I did so and got 27,657.. not what I was thinking.. I would assume I did something wrong here...

The SA RA wet bulb temps have to be looked up on the enthalpy chart; then subtract the lower enthalpy number from the higher enthalpy number.
Then multiply the CFM airflow * 4.5 if at sea level& that result times the enthalpy difference. That's supposed to give you the Btu.

I really recommend you take the time to learn how to do the calculations by hand, using a psychrometrics chart, and what it all means.

Once you gain a good understanding of it, retire the charts, and get a good psychrometrics app for your smart phone, preferably one that will calculate cooling and mixed air processes, and use it in the course of service calls.

You will be amazed at how it demystifies some problem systems, the system that is the subject of this thread is a prime example.
Unfortunately for the OP, there has been a 2.5 year parade of techs , including a manufacturers tech rep, that have utterly failed to diagnose the problem, even done thousands of dollars worth of useless repairs under warranty, because they either didn't take the air side readings necessary to see what the system was really doing, or they utterly failed to understand what the readings were telling them.

Sadly, even the most basic training in air side diagnostics is hard to come by in most areas.

Thank you very much for the words of wisdom. This is something I was never taught in school, so it rather overwhelming to comprehend at the moment. I talked to my service manager about using psychometric charts and calculations, he gave me a lot of good information on it, and showed me a few things. I am also signed up for a few classes next month paid by the company. Not to say I will be a pro at in the next month or two but I'm sure I will be better off.

Originally Posted by mark beiser

@ Trehak01

I really recommend you take the time to learn how to do the calculations by hand, using a psychrometrics chart, and what it all means.

Once you gain a good understanding of it, retire the charts, and get a good psychrometrics app for your smart phone, preferably one that will calculate cooling and mixed air processes, and use it in the course of service calls.

You will be amazed at how it demystifies some problem systems, the system that is the subject of this thread is a prime example.
Unfortunately for the OP, there has been a 2.5 year parade of techs , including a manufacturers tech rep, that have utterly failed to diagnose the problem, even done thousands of dollars worth of useless repairs under warranty, because they either didn't take the air side readings necessary to see what the system was really doing, or they utterly failed to understand what the readings were telling them.

Sadly, even the most basic training in air side diagnostics is hard to come by in most areas.

This is something I was never taught in school, so it rather overwhelming to comprehend at the moment.

The college program I went to had a 1 semester "Psychrometrics and Duct Sizing", class, but it didn't really cover psychrrometrics much, it was mainly about Manual J load calks, and Manual D duct design. Other than that, there was absolutely nothing taught about how to use psychrometrics, or air side diagnostics in general.

It always struck me as strange that most 2 year college and tech school HVAC programs teach almost nothing about AIR...

One thing that you will find immediately helpful in understanding things, and how to apply it on service calls in the field, is the Testo AC & Refrigeration Application Guide.

Mark, from what I have witnessed, we need a total retraining of service techs; few pay much if any attention to 'first & foremost' getting airflow right. I also believe they need to be certified as to, at the least, their knowledge. These horrible shortcomings need to be eliminated if we are to begin to reduce the wasteful use of energy...

I've seen some unbelievable A/C add-ons, on older belt-drive blower oil furnaces that will literally blow your mind when it comes to extreme low airflow; that should never happen to an HVAC consumer. Plus, most of them are left that way until a furnace change-out many, many long years later!

Few homes are energy efficiency rater/audited, & then after retro-work is done, have a room by room heat-gain heat-loss performed for proper equipment sizing & airflow to each room. Only the proper sequenced Best Practices will yield total optimal efficiency & optimally reduced energy utility bills.

I attended a trade school that mainly tough the basics of electricity and refrigeration.. I had to learn everything from there in the field. I spend most nights reading on this site and reading articles on subjects that trouble me most. If i had a call that I didn't get or didn't understand why something happen, more than likely you'll find me reading what I can when I get home. My education started when I started my first day of work.

I may or may not have read this. If it's a reciprocating 2 speed compressor. Bristol brand I believe had a problem shifting to high. I put about the same year model on this house and it worked great for a while, then would crap out and run again then crap out. Never not cooling, just not very well. It's a flaw with the compressors, I think there was some bulletin on them. I got a brand new unit for my customer with a scroll compressor. I had another one which was about a 2009 recip. They could get a brand new scroll for cost basically, they got a much better unit for a small amount more. When the crankshaft reverses positions in the compressor, it doesn't shift all the way as I recall. I think getting a little blow by in the 1st cylinder or not enough. I don't remember all the details, but was a problem.

Checking in for the new cooling season. This never got fixed (mediocre performance 2nd stage, supply air temp goes up about 5F from low to hi stage). Last season, TXV was replaced, 4" spacer inserted between blower and evap, and finally a new blower motor. Carrier footed the bill for most of that.

Unfortunately, the local Carrier rep has moved on, and I'm somewhat starting over trying to get Carrier re-engaged this season. Still think its that Bristol 2 stage compressor. I figure that Carrier can't now say everything is "within specs", otherwise they would not have spent the money doing those things last season.

I guess Carrier wants to save face, but it seems like they'd almost be money ahead just sending a whole new Infinity 16 or 17 2 stage scroll unit any time they have significant issues where a Bristol is involved. Carrier discontined this product for a reason. I think contractor didn't want to touch them anymore.

Checking in for the new cooling season. This never got fixed (mediocre performance 2nd stage, supply air temp goes up about 5F from low to hi stage). Last season, TXV was replaced, 4" spacer inserted between blower and evap, and finally a new blower motor. Carrier footed the bill for most of that.

Unfortunately, the local Carrier rep has moved on, and I'm somewhat starting over trying to get Carrier re-engaged this season. Still think its that Bristol 2 stage compressor. I figure that Carrier can't now say everything is "within specs", otherwise they would not have spent the money doing those things last season.

Will keep you updated.

I just read through this thread for the first time and there's no stifling a gut reaction to shake my head in disbelief until my neck is sore.

Bottom line is you need someone who knows refrigeration and airflow theory with experience and confidence. You have them here on this site but you don't have someone you know personally - yet - that you can pick up the phone, tell him to come over, and replace that damn compressor, even if you have to pay out of pocket for it.

If I were in your shoes I'd yank that Bristol out of there and install a Copeland Ultratech scroll in its place. Of course that might freak out the Infinity control, but it might not, given what it has been dealing with so far.

Something I noticed while reading earlier in the thread as to why capacity seemed worse in 2nd Stage vs. first...chalk it up to coil bypass factor. If the compressor is doing little to no more real work in 2nd stage, the only thing that changed was the indoor blower speed. That means you're moving more air across the evaporator with no increase in refrigeration capacity. The coil warms up, which would explain the modest increase in suction pressure with little change in head pressure. The 50% increase in amp draw can be attributed to perhaps a partial loading of the second stage cylinder. I'm inclined to agree with others who have stated the second stage valves are weak. I've seen weak valves on single stage compressors where the comp will still move refrigerant but the loss of capacity is just enough to bring comfort complaints. No reason why this can't be a similar situation with your Bristol TS.

Electricity makes refrigeration happen.

Refrigeration makes the HVAC psychrometric process happen.

HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.

I don't think retofit will work sicne it's a communicating unit and the condenser control board has logic specific for that 2 step recip. I'm not sure if the piping would even be sized right. You have ot gut the whole unit.

Better to just work hard with the distributor, contractor and Carrier to have mercy and swap out the whole condenser with a new Infinity 17 or 16 (can't remember if this was a heat pump) 2 stage scroll.

I don't think retofit will work sicne it's a communicating unit and the condenser control board has logic specific for that 2 step recip. I'm not sure if the piping would even be sized right. You have ot gut the whole unit.

Better to just work hard with the distributor, contractor and Carrier to have mercy and swap out the whole condenser with a new Infinity 17 or 16 (can't remember if this was a heat pump) 2 stage scroll.

You're probably right...my remark was made out of frustration for the OP's ongoing tragic saga of getting this resolved.

Funny how folks who design and sell stuff can't find anybody smart enough to fix it when something goes wrong.

Electricity makes refrigeration happen.

Refrigeration makes the HVAC psychrometric process happen.

HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.